1How to Get Your Patch Accepted Into the Hwmon Subsystem 2======================================================= 3 4This text is a collection of suggestions for people writing patches or 5drivers for the hwmon subsystem. Following these suggestions will greatly 6increase the chances of your change being accepted. 7 8 91. General 10---------- 11 12* It should be unnecessary to mention, but please read and follow: 13 14 - Documentation/process/submit-checklist.rst 15 - Documentation/process/submitting-drivers.rst 16 - Documentation/process/submitting-patches.rst 17 - Documentation/process/coding-style.rst 18 19* Please run your patch through 'checkpatch --strict'. There should be no 20 errors, no warnings, and few if any check messages. If there are any 21 messages, please be prepared to explain. 22 23* Please use the standard multi-line comment style. Do not mix C and C++ 24 style comments in a single driver (with the exception of the SPDX license 25 identifier). 26 27* If your patch generates checkpatch errors, warnings, or check messages, 28 please refrain from explanations such as "I prefer that coding style". 29 Keep in mind that each unnecessary message helps hiding a real problem, 30 and a consistent coding style makes it easier for others to understand 31 and review the code. 32 33* Please test your patch thoroughly. We are not your test group. 34 Sometimes a patch can not or not completely be tested because of missing 35 hardware. In such cases, you should test-build the code on at least one 36 architecture. If run-time testing was not achieved, it should be written 37 explicitly below the patch header. 38 39* If your patch (or the driver) is affected by configuration options such as 40 CONFIG_SMP, make sure it compiles for all configuration variants. 41 42 432. Adding functionality to existing drivers 44------------------------------------------- 45 46* Make sure the documentation in Documentation/hwmon/<driver_name>.rst is up to 47 date. 48 49* Make sure the information in Kconfig is up to date. 50 51* If the added functionality requires some cleanup or structural changes, split 52 your patch into a cleanup part and the actual addition. This makes it easier 53 to review your changes, and to bisect any resulting problems. 54 55* Never mix bug fixes, cleanup, and functional enhancements in a single patch. 56 57 583. New drivers 59-------------- 60 61* Running your patch or driver file(s) through checkpatch does not mean its 62 formatting is clean. If unsure about formatting in your new driver, run it 63 through Lindent. Lindent is not perfect, and you may have to do some minor 64 cleanup, but it is a good start. 65 66* Consider adding yourself to MAINTAINERS. 67 68* Document the driver in Documentation/hwmon/<driver_name>.rst. 69 70* Add the driver to Kconfig and Makefile in alphabetical order. 71 72* Make sure that all dependencies are listed in Kconfig. 73 74* Please list include files in alphabetic order. 75 76* Please align continuation lines with '(' on the previous line. 77 78* Avoid forward declarations if you can. Rearrange the code if necessary. 79 80* Avoid macros to generate groups of sensor attributes. It not only confuses 81 checkpatch, but also makes it more difficult to review the code. 82 83* Avoid calculations in macros and macro-generated functions. While such macros 84 may save a line or so in the source, it obfuscates the code and makes code 85 review more difficult. It may also result in code which is more complicated 86 than necessary. Use inline functions or just regular functions instead. 87 88* Limit the number of kernel log messages. In general, your driver should not 89 generate an error message just because a runtime operation failed. Report 90 errors to user space instead, using an appropriate error code. Keep in mind 91 that kernel error log messages not only fill up the kernel log, but also are 92 printed synchronously, most likely with interrupt disabled, often to a serial 93 console. Excessive logging can seriously affect system performance. 94 95* Use devres functions whenever possible to allocate resources. For rationale 96 and supported functions, please see Documentation/driver-api/driver-model/devres.rst. 97 If a function is not supported by devres, consider using devm_add_action(). 98 99* If the driver has a detect function, make sure it is silent. Debug messages 100 and messages printed after a successful detection are acceptable, but it 101 must not print messages such as "Chip XXX not found/supported". 102 103 Keep in mind that the detect function will run for all drivers supporting an 104 address if a chip is detected on that address. Unnecessary messages will just 105 pollute the kernel log and not provide any value. 106 107* Provide a detect function if and only if a chip can be detected reliably. 108 109* Only the following I2C addresses shall be probed: 0x18-0x1f, 0x28-0x2f, 110 0x48-0x4f, 0x58, 0x5c, 0x73 and 0x77. Probing other addresses is strongly 111 discouraged as it is known to cause trouble with other (non-hwmon) I2C 112 chips. If your chip lives at an address which can't be probed then the 113 device will have to be instantiated explicitly (which is always better 114 anyway.) 115 116* Avoid writing to chip registers in the detect function. If you have to write, 117 only do it after you have already gathered enough data to be certain that the 118 detection is going to be successful. 119 120 Keep in mind that the chip might not be what your driver believes it is, and 121 writing to it might cause a bad misconfiguration. 122 123* Make sure there are no race conditions in the probe function. Specifically, 124 completely initialize your chip and your driver first, then register with 125 the hwmon subsystem. 126 127* Use devm_hwmon_device_register_with_info() or, if your driver needs a remove 128 function, hwmon_device_register_with_info() to register your driver with the 129 hwmon subsystem. Try using devm_add_action() instead of a remove function if 130 possible. Do not use hwmon_device_register(). 131 132* Your driver should be buildable as module. If not, please be prepared to 133 explain why it has to be built into the kernel. 134 135* Do not provide support for deprecated sysfs attributes. 136 137* Do not create non-standard attributes unless really needed. If you have to use 138 non-standard attributes, or you believe you do, discuss it on the mailing list 139 first. Either case, provide a detailed explanation why you need the 140 non-standard attribute(s). 141 Standard attributes are specified in Documentation/hwmon/sysfs-interface.rst. 142 143* When deciding which sysfs attributes to support, look at the chip's 144 capabilities. While we do not expect your driver to support everything the 145 chip may offer, it should at least support all limits and alarms. 146 147* Last but not least, please check if a driver for your chip already exists 148 before starting to write a new driver. Especially for temperature sensors, 149 new chips are often variants of previously released chips. In some cases, 150 a presumably new chip may simply have been relabeled. 151